Video encoding device, video decoding device, video system, video encoding method, video decoding method, and computer readable storage medium

ABSTRACT

In the case where an input image is an image of a non-YUV420 format and an encoding unit is the smallest CU block, an adaptive-sub-sampling luma reference pixel acquisition unit sub-samples reference pixels existing neighboring a luma block corresponding to a chroma prediction target block based on a luma intra prediction mode, and acquires a pixel value of each of the sub-sampled reference pixels. In the case where the input image is an image of a non-YUV420 format and the encoding unit is the smallest CU block, an adaptive-sub-sampling chroma reference pixel acquisition unit sub-samples reference pixels existing neighboring the chroma prediction target block based on the luma intra prediction mode, and acquires a pixel value of each of the sub-sampled reference pixels.

This application is a continuation of International Patent ApplicationNo. PCT/JP2014/068405 filed on Jul. 10, 2014, and claims priority toJapanese Patent Application No. 2013-144726 filed on Jul. 10, 2013, theentire content of both of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to video encoding devices, video decodingdevices, video systems, video encoding methods, video decoding methods,and computer readable storage media.

BACKGROUND ART

HEVC (High Efficiency Video Coding) has been proposed as a videoencoding method using intra prediction, inter prediction, and residualtransform (e.g., see Non-patent reference 1).

[Configuration and Operations of Video Encoding Device MM]

FIG. 15 is a block diagram of a video encoding device MM according to aconventional example that codes a video image using the aforementionedvideo encoding method. The video encoding device MM includes an interprediction unit 10, an intra prediction unit 20, a transform andquantization unit 30, an entropy encoding unit 40, an inversequantization and inverse transform unit 50, an in-loop filtering unit60, a first buffer unit 70, and a second buffer unit 80.

An input image a and a later-described local decoded image g that issupplied from the first buffer unit 70 are input to the inter predictionunit 10. This inter prediction unit 10 performs inter prediction(inter-frame prediction) using the input image a and the local decodedimage g to generate and output an inter prediction image b.

The input image a and a later-described local decoded image f that issupplied from the second buffer unit 80 are input to the intraprediction unit 20. This intra prediction unit 20 performs intraprediction (intra-frame prediction) using the input image a and thelocal decoded image f to generate and output an intra prediction imagec.

An error (residual) signal between the input image a and the interprediction image b or the intra predication image c is input to thetransform and quantization unit 30. This transform and quantization unit30 transforms and quantizes the input residual signal to generate andoutput a quantization coefficient d.

The quantization coefficient d and side information (not shown) areinput to the entropy encoding unit 40. This entropy encoding unit 40performs entropy encoding on the input signal and outputs theentropy-coded signal as a bitstream z.

The quantization coefficient d is input to the inverse quantization andinverse transform unit 50. This inverse quantization and inversetransform unit 50 performs inverse quantization and inverse transform onthe quantization coefficient d to generate and output aninverse-transformed residual signal e.

The second buffer unit 80 accumulates the local decoded image f andsupplies the accumulated local decoded image f to the intra predictionunit 20 and the in-loop filtering unit 60 as appropriate. The localdecoded image f is a signal obtained by adding up the inter predictionimage b or the intra prediction image c and the inverse-transformedresidual signal e.

The local decoded image f is input to the in-loop filtering unit 60.This in-loop filtering unit 60 applies a filter such as a deblockingfilter to the local decoded image f to generate and output the localdecoded image g.

The first buffer unit 70 accumulates the local decoded image g andsupplies the accumulated local decoded image g to the inter predictionunit 10 as appropriate.

[Configuration and Operations of Video Decoding Device NN]

FIG. 16 is a block diagram of a video decoding device NN according to aconventional example that decodes a video image from the bitstream zgenerated by the video encoding device MM. The video decoding device NNincludes an entropy decoding unit 110, an inverse transform and inversequantization unit 120, an inter prediction unit 130, an intra predictionunit 140, an in-loop filter 150, a first buffer unit 160, and a secondbuffer unit 170.

The bitstream z is input to the entropy decoding unit 110. This entropydecoding unit 110 performs entropy decoding on the bitstream z, andgenerates and outputs a quantization coefficient B.

The inverse transform and inverse quantization unit 120, the interprediction unit 130, the intra prediction unit 140, the in-loopfiltering unit 150, the first buffer unit 160, and the second bufferunit 170 respectively operate similarly to the inverse quantization andinverse transform unit 50, the inter prediction unit 10, the intraprediction unit 20, the in-loop filtering unit 60, the first buffer unit70, and the second buffer unit 80 shown in FIG. 15.

(Details of Intra Prediction)

The aforementioned intra prediction will be described below in detail.Regarding intra prediction, Non-patent reference 1 indicates that pixelvalues in an encoding target block are predicted for each colorcomponent, using pixel values of reference pixels, which arereconstructed pixels that have already been encoded. Also, as lumacomponent prediction methods, a total of 35 modes, namely DC, Planar,and direction prediction for 33 directions are indicated as shown inFIG. 17. As chroma component prediction methods, a method using the sameprediction classification as that for a luma component, as well as DC,Planar, horizontal, and vertical methods that are independent from thosefor the luma component are indicated. With the above configuration,spatial redundancy can be reduced for each color component.

Non-patent reference 2 describes an LM mode as a technique for reducingredundancy among color components. For example, a case of using the LMmode for an image of a YUV420 format will now be described using FIG.18.

FIG. 18A shows chroma component pixels, and FIG. 18B shows lumacomponent pixels. In the LM mode, the chroma component is linearlypredicted using the luma component that have been reconstructed in thepixels denoted by 16 white circles in FIG. 18B and a prediction equationindicated as Equation (1) below.

[Equation 1]

pred_(c) [x,y]=α×((P _(L)[2x,2y]+P _(L)[2x,2y+1])>>1)+β  (1)

In Equation (1), P_(L) denotes a pixel value of the luma component, andpred_(c) denotes a predictive pixel value of the chroma component. α andβ respectively indicate parameters that can be obtained using referencepixels denoted by 8 black circles in FIG. 18A and 8 black circles inFIG. 18B, and are determined by Equations (2) and (3) below.

$\begin{matrix}{\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack {\alpha = \frac{R\left( {{\hat{P}}_{L},P_{C}^{\prime}} \right)}{R\left( {{\hat{P}}_{L},{\hat{P}}_{L}} \right)}}} & (2) \\{\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack {\beta = {{M\left( P_{C}^{\prime} \right)} - {\alpha \times {M\left( {\hat{P}}_{L} \right)}}}}} & (3)\end{matrix}$

R in Equation (2) denotes inner product calculation, M in Equation (3)denotes averaging calculation, and P′_(c) in Equations (2) and (3)denotes a pixel value of a reference pixel of the chroma component.P̂_(L) denotes a pixel value of the luma component obtained whileconsidering phases of the luma and the chroma, and is determined byEquation (4) below.

[Equation 4]

{circumflex over (P)} _(L) [x,y]=(P _(L)[2x,2y]+P _(L)[2x,2y+1])>>1  (4)

Note that the phase of the reference pixel in the upper part remainsshifted in order to reduce memory access. The chroma prediction isperformed for each smallest processing block, which is called a TU(Transform Unit).

In the case of extending the LM mode for an image of the aforementionedYUV420 format and using the extended LM mode for an image of a YUV422format, the number of reference pixels in the vertical directionincreases as shown in FIG. 19.

FIG. 20 is a block diagram of the intra prediction units 20 and 140 thatperform intra prediction using the aforementioned LM mode. The intraprediction units 20 and 140 each include a luma reference pixelacquisition unit 21, a chroma reference pixel acquisition unit 22, aprediction coefficient derivation unit 23, and a chroma linearprediction unit 24.

The luma component of the local decoded image f is input to the lumareference pixel acquisition unit 21. This luma reference pixelacquisition unit 21 acquires a pixel value of each reference pixelexisting neighboring a luma block corresponding to a chroma predictiontarget block, adjusts the phase of the acquired pixel value, and outputsthe phase-adjusted pixel value as a luma reference pixel value h.

The chroma component of the local decoded image f is input to the chromareference pixel acquisition unit 22. This chroma reference pixelacquisition unit 22 acquires a pixel value of each reference pixelexisting neighboring the chroma prediction target block, and outputs theacquired pixel value as a chroma reference pixel value i.

The luma reference pixel value h and the chroma reference pixel value iare input to the prediction coefficient derivation unit 23. Thisprediction coefficient derivation unit 23 obtains the parameters α and βfrom Equations (2) to (4) above using these input pixel values, andoutputs the parameters α and β as prediction coefficients j.

The luma component of the local decoded image f and the predictioncoefficients j are input to the chroma linear prediction unit 24. Thischroma linear prediction unit 24 obtains a predictive pixel value of thechroma component by Equation (1) above using these input signals, andoutputs the obtained predictive pixel value as a chroma predictive pixelvalue k.

Incidentally, the available memory capacity is increasing with theadvance of the semiconductor technology. However, with the increase ofthe memory capacity, the granularity of memory access becomes large.Meanwhile, the memory bandwidth has not been significantly widenedcompared with the increase of the memory capacity. Since the memory isused in encoding and decoding of video images, the granularity of thememory access and the memory bandwidth have been bottlenecks.

In addition, manufacturing costs and power consumption of a memory thatis closest to a calculation core (e.g., an SRAM) are higher than thoseof an external memory (e.g., a DRAM). For this reason, it is favorablethat the memory capacity of the memory closest to the calculation corecan be reduced as much as possible. However, since video images need tobe able to be decoded even with the worst value provided in thespecifications, the memory closest to the calculation core needs to beable to satisfy memory requirements at the worst value, rather thanaverage memory requirements (granularity, size, and number etc.).

In the LM mode, since the parameters are derived for each TU asmentioned above, the number of reference pixels increases, and thenumber of times of calculation and the number of times of memory accessbecome large.

For example, the number of times of calculation and the number ofreference pixels for deriving the parameters in the case of using the LMmode for an image of the YUV420 format will be considered below. Thesize of an LCU (Largest Encoding unit), which is the largest processingblock, is provided as 64×64 in the main profile in Non-patent reference1, and the size of the smallest CU, which is the smallest processingblock, is 4×4. In addition, since the number of chroma pixels in theYUV420 format is ¼, the smallest calculation block of the luma componentis 8×8. For this reason, the number of times of calculation for derivingthe parameters is (64/8)²=64 times, and the number of reference pixelsis 28×64.

Non-patent reference 2 describes a technique for deriving the parametersfor each CU (Encoding unit) in order to reduce the worst value of thenumber of times of calculation for deriving the parameters for an imageof a non-YUV420 format. FIG. 21 shows the number of times of calculationand the number of reference pixels in the case of deriving theparameters for each TU and in the case of deriving the parameters foreach CU.

As described above, redundancy among color components can be reduced inthe LM mode. However, when considering the CTU units, a problem arisesin that the number of reference pixels of the worst value used whenderiving the parameters is large.

Non-patent reference 3 describes a technique for reducing the number ofreference pixels in the LM mode for an image of a non-YUV420 format.

For example, a case of applying the technique in Non-patent reference 3to an image of a YUV422 format will be described using FIG. 22. In thiscase, the number of reference pixels neighboring the long side of aprediction target block is half compared with the case shown in FIG. 19.For this reason, as shown in FIG. 24, both the number of luma referencepixels and the number of chroma reference pixels are 8 pixels.

Also, a case of applying the technique in Non-patent reference 3 to animage of a YUV444 format will be described using FIG. 23. In this caseas well, the number of reference pixels neighboring the long side of aprediction target block is half. For this reason, as shown in FIG. 24,both the number of luma reference pixels and the number of chromareference pixels are 8 pixels.

PRIOR ART DOCUMENT(S) Non-Patent Reference

-   Non-patent reference 1: JCTVC-L1003, High Efficiency Video Coding    (HEVC) Range Extensions text specification: Draft 2 (for PDAM).-   Non-patent reference 2: JCTVC-M0097, RCE1: The performance of    extended chroma mode for non-4:2:0 format.-   Non-patent reference 3: JCTVC-M0412, AHG5: CU based chroma intra    prediction with reduced reference.

DISCLOSURE OF INVENTION Problems that the Invention is to Solve

The technique described in Non-patent reference 3 achieves a reductionin the number of reference pixels by uniformly sub-sampling thereference pixels. For this reason, when sub-sampling the referencepixels, characteristics of images are not considered, and there is apossibility of degradation in encoding performance.

The present invention has been made in view of the foregoing problem,and an object of the invention is to reduce the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents, while suppressing degradation in encoding performance.

Means of Solving the Problems

In order to solve the foregoing problem, the present invention proposesthe following items.

(1) The invention proposes a video encoding device (corresponding, forexample, to a video encoding device AA in FIG. 1) that codes a videoimage configured to include a plurality of color components, including:an intra-frame prediction unit (corresponding, for example, to an intraprediction unit 20A in FIG. 1) for performing intra-frame prediction,the intra-frame prediction unit including: an adaptive-sub-sampling lumareference pixel sub-sampling unit (corresponding, for example, to anadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2) for sub-sampling reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; an adaptive-sub-sampling luma reference pixelacquisition unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2) for acquiring a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; an adaptive-sub-sampling chroma reference pixelsub-sampling unit (corresponding, for example, to anadaptive-sub-sampling chroma reference pixel acquisition unit 22A inFIG. 2) for sub-sampling reference pixels existing neighboring thechroma prediction target block based on the luma intra prediction mode;an adaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2) for acquiring a pixelvalue of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; aprediction coefficient derivation unit (corresponding, for example, to aprediction coefficient derivation unit 23 in FIG. 2) for deriving aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a chroma linear prediction unit (corresponding,for example, to a chroma linear prediction unit 24 in FIG. 2) forlinearly predicting a predictive pixel value of each pixel constitutingthe chroma prediction target block, using a local decoded pixel value ofthe luma block corresponding to the chroma prediction target block andthe prediction coefficient derived by the prediction coefficientderivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(2) Regarding the video encoding device in (1), the present inventionproposes a video encoding device in which the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit perform the sub-sampling only in acase where a encoding unit is a predetermined smallest encoding unit.

According to this invention, in the video encoding device in (1), theaforementioned sub-sampling is performed only in the case where theencoding unit is the predetermined smallest encoding unit. For thisreason, the number of reference pixels to be referenced in order toreduce redundancy among color components can be reduced only in the casewhere the encoding unit is the predetermined smallest encoding unit.

(3) Regarding the video encoding device in (1), the present inventionproposes a video encoding device in which the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit always perform the sub-samplingregardless of a encoding unit.

According to this invention, in the video encoding device in (1), theaforementioned sub-sampling is always performed regardless of theencoding unit. For this reason, the number of reference pixels to bereferenced in order to reduce redundancy among color components canalways be reduced regardless of the encoding unit.

(4) Regarding any of the video encoding devices in (1) to (3), thepresent invention proposes a video encoding device in which theadaptive-sub-sampling luma reference pixel sub-sampling unit and theadaptive-sub-sampling chroma reference pixel sub-sampling unit performthe sub-sampling and reduce the number of reference pixels to 1/n (wheren is any power of two that satisfies n>0) of the number of referencepixels before the sub-sampling.

According to this invention, in any of the video encoding devices in (1)to (3), by sub-sampling the reference pixels, the number of referencepixels is reduced to 1/n of the number of reference pixels before thesub-sampling. For this reason, it is possible to adjust suppressingdegradation in encoding performance and a decrease of the number ofreference pixels to be referenced in order to reduce redundancy amongcolor components, by setting the value of n.

(5) Regarding any of the video encoding devices in (1) to (4), thepresent invention proposes a video encoding device in which the videoimage is a video image of a YUV422 format.

According to this invention, in any of the video encoding devices in (1)to (4), the video image is a video image of a YUV422 format. For thisreason, even if a pixel block of the chroma component is rectangular inthe video image of a YUV422 format, the reference pixels can besub-sampled such that the number thereof becomes a power of two, andtherefore, operations such as division can be achieved with shiftoperation.

(6) Regarding any of the video encoding devices in (1) to (5), thepresent invention proposes a video encoding device in which the size ofa processing block is 8×8.

Here, in the case where the size of the processing block is 4×4, thereference pixels are excessively sub-sampled, and accordingly theaccuracy of the prediction coefficient decreases, and the number oftimes of operation in a CTU (64×64) is 16×16=256, which is too many. Incontrast, in the case where the size of the processing block is 16×16,the reference pixels are not excessively sub-sampled, and therefore theaccuracy of the prediction coefficient increases, whereas the encodingperformance degrades since detailed characteristics of the processingblock cannot be reflected.

For this reason, according to this invention, in any of the videoencoding devices in (1) to (5), the size of the processing block is 8×8.For this reason, the accuracy of the prediction coefficient can beincreased while not excessively sub-sampling the reference pixels, andit is also possible to reflect detailed characteristics of theprocessing block while suppressing the number of times of operation ineach CTU, and increase the encoding performance.

(7) The invention proposes A video decoding device (corresponding, forexample, to a video decoding device BB in FIG. 9) that decodes a videoimage configured to include a plurality of color components, including:an intra-frame prediction unit (corresponding, for example, to an intraprediction unit 140A in FIG. 9) for performing intra-frame prediction,the intra-frame prediction unit including: an adaptive-sub-sampling lumareference pixel sub-sampling unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2) for sub-sampling reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; an adaptive-sub-sampling luma reference pixelacquisition unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2) for acquiring a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; an adaptive-sub-sampling chroma reference pixelsub-sampling unit (corresponding, for example, to theadaptive-sub-sampling chroma reference pixel acquisition unit 22A inFIG. 2) for sub-sampling reference pixels existing neighboring thechroma prediction target block based on the luma intra prediction mode;an adaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2) for acquiring a pixelvalue of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; aprediction coefficient derivation unit (corresponding, for example, tothe prediction coefficient derivation unit 23 in FIG. 2) for deriving aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a chroma linear prediction unit (corresponding,for example, to the chroma linear prediction unit 24 in FIG. 2) forlinearly predicting a predictive pixel value of each pixel constitutingthe chroma prediction target block, using a local decoded pixel value ofthe luma block corresponding to the chroma prediction target block andthe prediction coefficient derived by the prediction coefficientderivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(8) Regarding the video decoding device in (7), the present inventionproposes a video decoding device in which the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit perform the sub-sampling only in acase where a decoding unit is a predetermined smallest decoding unit.

According to this invention, in the video decoding device in (7), theaforementioned sub-sampling is performed only in the case where thedecoding unit is the predetermined smallest decoding unit. For thisreason, the number of reference pixels to be referenced in order toreduce redundancy among color components can be reduced only in the casewhere the decoding unit is the predetermined smallest decoding unit.

(9) Regarding the video decoding device in (7), the present inventionproposes a video decoding device in which the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit always perform the sub-samplingregardless of a decoding unit.

According to this invention, in the video decoding device in (7), theaforementioned sub-sampling is always performed regardless of thedecoding unit. For this reason, the number of reference pixels to bereferenced in order to reduce redundancy among color components canalways be reduced regardless of the decoding unit.

(10) Regarding any of the video decoding devices in (7) to (9), thepresent invention proposes a video decoding device in which theadaptive-sub-sampling luma reference pixel sub-sampling unit and theadaptive-sub-sampling chroma reference pixel sub-sampling unit performthe sub-sampling and reduce the number of reference pixels to 1/n (wheren is any power of two that satisfies n>0) of the number of referencepixels before the sub-sampling.

According to this invention, in any of the video decoding devices in (7)to (9), by sub-sampling the reference pixels, the number of referencepixels is reduced to 1/n of the number of reference pixels before thesub-sampling. For this reason, it is possible to adjust suppressingdegradation in encoding performance and a decrease of the number ofreference pixels to be referenced in order to reduce redundancy amongcolor components, by setting the value of n.

(11) Regarding any of the video decoding devices in (7) to (10), thepresent invention proposes a video decoding device in which the videoimage is a video image of a YUV422 format.

According to this invention, in any of the video decoding devices in (7)to (10), the video image is a video image of a YUV422 format. For thisreason, even if a pixel block of the chroma component is rectangular inthe video image of a YUV422 format, the number of reference pixels canbe sub-sampled so as to become a power of two, and therefore, operationssuch as division can be achieved with shift operation.

(12) Regarding any of the video decoding devices in (7) to (11), thepresent invention proposes a video decoding device in which the size ofa processing block is 8×8.

Here, in the case where the size of the processing block is 4×4, thereference pixels are excessively sub-sampled, and accordingly theaccuracy of the prediction coefficient decreases, and the number oftimes of operation in a CTU (64×64) is 16×16=256, which is too many. Incontrast, in the case where the size of the processing block is 16×16,the reference pixels are not excessively sub-sampled, and therefore theaccuracy of the prediction coefficient increases, whereas the encodingperformance degrades since detailed characteristics of the processingblock cannot be reflected.

For this reason, according to this invention, in any of the videoencoding devices in (7) to (11), the size of the processing block is8×8. For this reason, the accuracy of the prediction coefficient can beincreased while not excessively sub-sampling the reference pixels, andit is also possible to reflect detailed characteristics of theprocessing block while suppressing the number of times of operation ineach CTU, and increase the encoding performance.

(13) The present invention proposes a video system including a videoencoding device (corresponding, for example, to the video encodingdevice AA in FIG. 1) that codes a video image configured to include aplurality of color components, and a video decoding device(corresponding, for example, to the video decoding device BB in FIG. 9)that decodes a video image configured to include a plurality of colorcomponents, the video encoding device including an encoding-sideintra-frame prediction unit (corresponding, for example, to the intraprediction unit 20A in FIG. 1) for performing intra-frame prediction,the encoding-side intra-frame prediction unit including: a coding-sideadaptive-sub-sampling luma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2) for sub-sampling reference pixelsexisting neighboring a luma block corresponding to a chroma predictiontarget block based on a luma intra prediction mode; a coding-sideadaptive-sub-sampling luma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2) for acquiring a pixel value of areference pixel after the sub-sampling performed by the encoding-sideadaptive-sub-sampling luma reference pixel sub-sampling unit; acoding-side adaptive-sub-sampling chroma reference pixel sub-samplingunit (corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2) for sub-samplingreference pixels existing neighboring the chroma prediction target blockbased on the luma intra prediction mode; a coding-sideadaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2) for acquiring a pixelvalue of a reference pixel after the sub-sampling performed by theencoding-side adaptive-sub-sampling chroma reference pixel sub-samplingunit; a coding-side prediction coefficient derivation unit(corresponding, for example, to the prediction coefficient derivationunit 23 in FIG. 2) for deriving a prediction coefficient using the pixelvalue acquired by the encoding-side adaptive-sub-sampling luma referencepixel acquisition unit and the pixel value acquired by the encoding-sideadaptive-sub-sampling chroma reference pixel acquisition unit; and acoding-side chroma linear prediction unit (corresponding, for example,to the chroma linear prediction unit 24 in FIG. 2) for linearlypredicting a predictive pixel value of each pixel constituting thechroma prediction target block, using a local decoded pixel value of theluma block corresponding to the chroma prediction target block, and theprediction coefficient derived by the encoding-side predictioncoefficient derivation unit, the video decoding device including adecoding-side intra-frame prediction unit (corresponding, for example,to the intra prediction unit 140A in FIG. 9) for performing intra-frameprediction, the decoding-side intra-frame prediction unit including: adecoding-side adaptive-sub-sampling luma reference pixel sub-samplingunit (corresponding, for example, to the adaptive-sub-sampling lumareference pixel acquisition unit 21A in FIG. 2) for sub-samplingreference pixels existing neighboring a luma block corresponding to achroma prediction target block based on the luma intra prediction mode;a decoding-side adaptive-sub-sampling luma reference pixel acquisitionunit (corresponding, for example, to the adaptive-sub-sampling lumareference pixel acquisition unit 21A in FIG. 2) for acquiring a pixelvalue of a reference pixel after the sub-sampling performed by thedecoding-side adaptive-sub-sampling luma reference pixel sub-samplingunit; decoding-side adaptive-sub-sampling chroma reference pixelsub-sampling unit (corresponding, for example, to theadaptive-sub-sampling chroma reference pixel acquisition unit 22A inFIG. 2) for sub-sampling reference pixels existing neighboring thechroma prediction target block based on the luma intra prediction mode;a decoding-side adaptive-sub-sampling chroma reference pixel acquisitionunit (corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2) for acquiring a pixelvalue of a reference pixel after the sub-sampling performed by thedecoding-side adaptive-sub-sampling chroma reference pixel sub-samplingunit; a decoding-side prediction coefficient derivation unit(corresponding, for example, to the prediction coefficient derivationunit 23 in FIG. 2) for deriving a prediction coefficient using the pixelvalue acquired by the decoding-side adaptive-sub-sampling luma referencepixel acquisition unit and the pixel value acquired by the decoding-sideadaptive-sub-sampling chroma reference pixel acquisition unit; and adecoding-side chroma linear prediction unit (corresponding, for example,to the chroma linear prediction unit 24 in FIG. 2) for linearlypredicting a predictive pixel value of each pixel constituting thechroma prediction target block, using a local decoded pixel value of theluma block corresponding to the chroma prediction target block and theprediction coefficient derived by the decoding-side predictioncoefficient derivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(14) The invention proposes a method for encoding a video image in avideo encoding device (corresponding, for example, to the video encodingdevice AA in FIG. 1) that codes a video image configured to include aplurality of color components, the video encoding device including anintra-frame prediction unit (corresponding, for example, to the intraprediction unit 20A in FIG. 1) for performing intra-frame prediction andhaving: an adaptive-sub-sampling luma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2); an adaptive-sub-sampling lumareference pixel acquisition unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2); an adaptive-sub-sampling chroma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); anadaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); a predictioncoefficient derivation unit (corresponding, for example, to theprediction coefficient derivation unit 23 in FIG. 2); and a chromalinear prediction unit (corresponding, for example, to the chroma linearprediction unit 24 in FIG. 2), the method including: a first step inwhich the adaptive-sub-sampling luma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; a second step in which the adaptive-sub-sampling lumareference pixel acquisition unit acquires a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; a third step in which theadaptive-sub-sampling chroma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring the chroma predictiontarget block based on the luma intra prediction mode; a fourth step inwhich the adaptive-sub-sampling chroma reference pixel acquisition unitacquires a pixel value of a reference pixel after the sub-samplingperformed by the adaptive-sub-sampling chroma reference pixelsub-sampling unit; a fifth step in which the prediction coefficientderivation unit derives a prediction coefficient using the pixel valueacquired by the adaptive-sub-sampling luma reference pixel acquisitionunit and the pixel value acquired by the adaptive-sub-sampling chromareference pixel acquisition unit; and a sixth step in which the chromalinear prediction unit linearly predicts a predictive pixel value ofeach pixel constituting the chroma prediction target block, using alocal decoded pixel value of the luma block corresponding to the chromaprediction target block and the prediction coefficient derived by theprediction coefficient derivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(15) The invention proposes a method for decoding a video image in avideo decoding device (corresponding, for example, to the video decodingdevice BB in FIG. 9) that decodes a video image configured to include aplurality of color components, the video decoding device including anintra-frame prediction unit (corresponding, for example, to the intraprediction unit 140A in FIG. 9) for performing intra-frame predictionand having: an adaptive-sub-sampling luma reference pixel sub-samplingunit (corresponding, for example, to the adaptive-sub-sampling lumareference pixel acquisition unit 21A in FIG. 2); anadaptive-sub-sampling luma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2); an adaptive-sub-sampling chromareference pixel sub-sampling unit (corresponding, for example, to theadaptive-sub-sampling chroma reference pixel acquisition unit 22A inFIG. 2); an adaptive-sub-sampling chroma reference pixel acquisitionunit (corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); a predictioncoefficient derivation unit (corresponding, for example, to theprediction coefficient derivation unit 23 in FIG. 2); and a chromalinear prediction unit (corresponding, for example, to the chroma linearprediction unit 24 in FIG. 2), the method including: a first step inwhich the adaptive-sub-sampling luma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; a second step in which the adaptive-sub-sampling lumareference pixel acquisition unit acquires a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; a third step in which theadaptive-sub-sampling chroma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring the chroma predictiontarget block based on the luma intra prediction mode; a fourth step inwhich the adaptive-sub-sampling chroma reference pixel acquisition unitacquires a pixel value of a reference pixel after the sub-samplingperformed by the adaptive-sub-sampling chroma reference pixelsub-sampling unit; a fifth step in which the prediction coefficientderivation unit derives a prediction coefficient using the pixel valueacquired by the adaptive-sub-sampling luma reference pixel acquisitionunit and the pixel value acquired by the adaptive-sub-sampling chromareference pixel acquisition unit; and a sixth step in which the chromalinear prediction unit linearly predicts a predictive pixel value ofeach pixel constituting the chroma prediction target block, using alocal decoded pixel value of the luma block corresponding to the chromaprediction target block and the prediction coefficient derived by theprediction coefficient derivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(16) The present invention proposes a non-transitory computer readablestorage medium storing a program for causing a computer to execute amethod for encoding a video image in a video encoding device(corresponding, for example, to the video encoding device AA in FIG. 1)that codes a video image configured to include a plurality of colorcomponents, the video encoding device including an intra-frameprediction unit (corresponding, for example, to the intra predictionunit 20A in FIG. 1) for performing intra-frame prediction and having: anadaptive-sub-sampling luma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2); an adaptive-sub-sampling lumareference pixel acquisition unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2); an adaptive-sub-sampling chroma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); anadaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); a predictioncoefficient derivation unit (corresponding, for example, to theprediction coefficient derivation unit 23 in FIG. 2); and a chromalinear prediction unit (corresponding, for example, to the chroma linearprediction unit 24 in FIG. 2), the method including: a first step inwhich the adaptive-sub-sampling luma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; a second step in which the adaptive-sub-sampling lumareference pixel acquisition unit acquires a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; a third step in which theadaptive-sub-sampling chroma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring the chroma predictiontarget block based on the luma intra prediction mode; a fourth step inwhich the adaptive-sub-sampling chroma reference pixel acquisition unitacquires a pixel value of a reference pixel after the sub-samplingperformed by the adaptive-sub-sampling chroma reference pixelsub-sampling unit; a fifth step in which the prediction coefficientderivation unit derives a prediction coefficient using the pixel valueacquired by the adaptive-sub-sampling luma reference pixel acquisitionunit and the pixel value acquired by the adaptive-sub-sampling chromareference pixel acquisition unit; and a sixth step in which the chromalinear prediction unit linearly predicts a predictive pixel value ofeach pixel constituting the chroma prediction target block, using alocal decoded pixel value of the luma block corresponding to the chromaprediction target block and the prediction coefficient derived by theprediction coefficient derivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

(17) The present invention proposes a non-transitory computer readablestorage medium storing a program for causing a computer to execute amethod for decoding a video image in a video decoding device(corresponding, for example, to the video decoding device BB in FIG. 9)that decodes a video image configured to include a plurality of colorcomponents, the video decoding device including an intra-frameprediction unit (corresponding, for example, to the intra predictionunit 140A in FIG. 9) for performing intra-frame prediction and having:an adaptive-sub-sampling luma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling luma referencepixel acquisition unit 21A in FIG. 2); an adaptive-sub-sampling lumareference pixel acquisition unit (corresponding, for example, to theadaptive-sub-sampling luma reference pixel acquisition unit 21A in FIG.2); an adaptive-sub-sampling chroma reference pixel sub-sampling unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); anadaptive-sub-sampling chroma reference pixel acquisition unit(corresponding, for example, to the adaptive-sub-sampling chromareference pixel acquisition unit 22A in FIG. 2); a predictioncoefficient derivation unit (corresponding, for example, to theprediction coefficient derivation unit 23 in FIG. 2); and a chromalinear prediction unit (corresponding, for example, to the chroma linearprediction unit 24 in FIG. 2), the method including: a first step inwhich the adaptive-sub-sampling luma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; a second step in which the adaptive-sub-sampling lumareference pixel acquisition unit acquires a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; a third step in which theadaptive-sub-sampling chroma reference pixel sub-sampling unitsub-samples reference pixels existing neighboring the chroma predictiontarget block based on the luma intra prediction mode; a fourth step inwhich the adaptive-sub-sampling chroma reference pixel acquisition unitacquires a pixel value of a reference pixel after the sub-samplingperformed by the adaptive-sub-sampling chroma reference pixelsub-sampling unit; a fifth step in which the prediction coefficientderivation unit derives a prediction coefficient using the pixel valueacquired by the adaptive-sub-sampling luma reference pixel acquisitionunit and the pixel value acquired by the adaptive-sub-sampling chromareference pixel acquisition unit; and a sixth step in which the chromalinear prediction unit linearly predicts a predictive pixel value ofeach pixel constituting the chroma prediction target block, using alocal decoded pixel value of the luma block corresponding to the chromaprediction target block and the prediction coefficient derived by theprediction coefficient derivation unit.

According to this invention, in the intra-frame prediction, thereference pixels existing neighboring the luma block corresponding tothe chroma prediction target block and the reference pixels existingneighboring the chroma prediction target block are sub-sampled based onthe luma intra prediction mode. For this reason, the reference pixelscan be sub-sampled based on a luma component prediction method, andtherefore the number of pixels to be referenced in order to reduceredundancy among color components can be halved, while consideringcharacteristics of the image. Accordingly, the number of referencepixels to be referenced in order to reduce redundancy among colorcomponents can be reduced, while suppressing degradation in encodingperformance.

Effects of the Invention

According to the present invention, the number of reference pixels to bereferenced in order to reduce redundancy among color components can bereduced, while suppressing degradation in encoding performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a video encoding device according to afirst embodiment of the present invention;

FIG. 2 is a block diagram of an intra prediction unit provided in thevideo encoding device according to the aforementioned embodiment;

FIG. 3 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 4 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 5 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 6 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 7 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 8 is a diagram for illustrating operations of the intra predictionunit provided in the video encoding device according to theaforementioned embodiment;

FIG. 9 is a block diagram of a video decoding device according to thefirst embodiment of the present invention;

FIG. 10 is a diagram for illustrating operations of an intra predictionunit provided in a video encoding device according to a secondembodiment of the present invention;

FIG. 11 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a modification of the present invention;

FIG. 12 is a diagram for illustrating operations of the intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a modification of the present invention;

FIG. 13 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a modification of the present invention;

FIG. 14 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a modification of the present invention;

FIG. 15 is a block diagram of a video encoding device according to aconventional example;

FIG. 16 is a block diagram of a video decoding device according to aconventional example;

FIG. 17 is a diagram for illustrating a luma component predictionmethod;

FIG. 18 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example;

FIG. 19 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example;

FIG. 20 is a block diagram of an intra prediction unit provided in avideo encoding device and a video decoding device according to aconventional example;

FIG. 21 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example;

FIG. 22 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example;

FIG. 23 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example; and

FIG. 24 is a diagram for illustrating operations of intra predictionunits provided in a video encoding device and a video decoding deviceaccording to a conventional example.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, modes for carrying out the present invention will bedescribed with reference to the drawings. Note that constituent elementsin the following embodiments can be replaced with existing constituentelements or the like as appropriate, and various variations includingcombinations with other existing constituent elements are possible.Accordingly, the descriptions of the following embodiments do not limitthe content of the invention stated in the claims.

First Embodiment Configuration and Operations of Video Encoding DeviceAA

FIG. 1 is a block diagram of a video encoding device AA according to afirst embodiment of the present invention. The video encoding device AAis different from the video encoding device MM according to theconventional example shown in FIG. 15 in that an intra prediction unit20A is provided in place of the intra prediction unit 20. Note that thesame constituent elements of the video encoding device AA as those ofthe video encoding device MM are assigned the same signs, anddescriptions thereof will be omitted.

FIG. 2 is a block diagram of the intra prediction unit 20A. The intraprediction unit 20A is different from the intra prediction unit 20according to the conventional example shown in FIG. 20 in that anadaptive-sub-sampling luma reference pixel acquisition unit 21A isprovided in place of the luma reference pixel acquisition unit 21, andin that an adaptive-sub-sampling chroma reference pixel acquisition unit22A is provided in place of the chroma reference pixel acquisition unit22.

A luma component of a local decoded image f is input to theadaptive-sub-sampling luma reference pixel acquisition unit 21A. Thisadaptive-sub-sampling luma reference pixel acquisition unit 21A performsprocessing appropriate for the encoding unit, and generates and outputsa luma reference pixel value h.

Specifically, in the case where the encoding unit is other than thesmallest CU block, which is the smallest encoding unit of CUs, theadaptive-sub-sampling luma reference pixel acquisition unit 21A acquiresa pixel value of each reference pixel existing neighboring a luma blockcorresponding to a chroma prediction target block, adjusts the phasethereof, and outputs the phase-adjusted pixel value as a luma referencepixel value h.

On the other hand, in the case where an input image a is an image of anon-YUV420 format and the encoding unit is the smallest CU block, theadaptive-sub-sampling luma reference pixel acquisition unit 21Ainitially determines a luma intra prediction mode such that the inputimage a is most resembled using the local decoded image f. Next, theadaptive-sub-sampling luma reference pixel acquisition unit 21Asub-samples reference pixels existing neighboring the luma blockcorresponding to the chroma prediction target block based on the lumaintra prediction mode, acquires a pixel value of each of the sub-sampledreference pixels, and outputs the acquired pixel value as a lumareference pixel value h.

A chroma component of the local decoded image f is input to theadaptive-sub-sampling chroma reference pixel acquisition unit 22A. Thisadaptive-sub-sampling chroma reference pixel acquisition unit 22Aperforms processing appropriate for the encoding unit, and generates andoutputs a chroma reference pixel value i.

Specifically, in the case where the encoding unit is other than thesmallest CU block, the adaptive-sub-sampling chroma reference pixelacquisition unit 22A acquires a pixel value of each reference pixelexiting neighboring the chroma prediction target block, and outputs theacquired pixel value as the chroma reference pixel value i.

On the other hand, in the case where the input image a is an image of anon-YUV420 format and the encoding unit is the smallest CU block, theadaptive-sub-sampling chroma reference pixel acquisition unit 22Ainitially determines a luma intra prediction mode such that the inputimage a is most resembled using the local decoded image f. Next, theadaptive-sub-sampling chroma reference pixel acquisition unit 22Asub-samples the reference pixels existing neighboring the chromaprediction target block based on the luma intra prediction mode,acquires a pixel value of each of the sub-sampled reference pixels, andoutputs the acquired pixel value as a chroma reference pixel value i.

The sub-sampling of the reference pixels based on the luma intraprediction mode performed by the adaptive-sub-sampling luma referencepixel acquisition unit 21A and the adaptive-sub-sampling chromareference pixel acquisition unit 22A will be described below. Here, theluma component prediction method can be determined by referencing theluma intra prediction mode.

For this reason, in the case where the luma component prediction methodis DC, Planar, or direction prediction for an oblique direction, theadaptive-sub-sampling luma reference pixel acquisition unit 21Auniformly sub-samples the reference pixels existing neighboring the lumablock corresponding to the chroma prediction target block to acquirepixel values of the sub-sampled reference pixels, and theadaptive-sub-sampling chroma reference pixel acquisition unit 22Auniformly sub-samples the reference pixels existing neighboring thechroma prediction target block to acquire pixel values of thesub-sampled reference pixels. Regarding this case, FIG. 3 shows a casewhere the input image a is an image of a YUV422 format, and FIG. 6 showsa case where the input image a is an image of a YUV444 format. FIGS. 3and 6 indicate that, as a result of the reference pixels being uniformlysub-sampled, the pixel value of every other reference pixel is acquired.Note that the case of direction prediction for an oblique directionrefers to the case of prediction modes 15 to 21 in FIG. 17.

In the case where the luma component prediction method is prediction fora horizontal direction or a direction close to a horizontal direction,the adaptive-sub-sampling luma reference pixel acquisition unit 21Aacquires pixel values of only reference pixels on the left side of theluma block corresponding to the chroma prediction target block, and theadaptive-sub-sampling chroma reference pixel acquisition unit 22Aacquires pixel values of only reference pixels on the left side of thechroma prediction target block. Regarding this case, FIG. 4 shows a casewhere the input image a is an image of a YUV422 format, and FIG. 7 showsa case where the input image a is an image of a YUV444 format. Note thatthe case of prediction for a horizontal direction or a direction closeto a horizontal direction refers to the case of prediction modes 2 to 14in FIG. 17.

In the case where the luma component prediction method is prediction fora vertical direction or a direction close to a vertical direction, theadaptive-sub-sampling luma reference pixel acquisition unit 21A acquirespixel values of only reference pixels above the luma block correspondingto the chroma prediction target block, and the adaptive-sub-samplingchroma reference pixel acquisition unit 22A acquires pixel values ofonly reference pixels above the chroma prediction target block.Regarding this case, FIG. 5 shows a case where the input image a is animage of a YUV422 format, and FIG. 8 shows a case where the input imagea is an image of a YUV444 format. Note that the case of prediction for avertical direction or a direction close to a vertical direction refersto the case of prediction modes 22 to 34 in FIG. 17.

[Configuration and Operations of Video Decoding Device BB]

FIG. 9 is a block diagram of a video decoding device BB according to thefirst embodiment of the present invention. The video decoding device BBis different from the video decoding device NN according to theconventional example shown in FIG. 16 in that an intra prediction unit140A is provided in place of the intra prediction unit 140. Note thatthe same constituent elements of the video decoding device BB as thoseof the video decoding device NN are assigned the same signs, anddescriptions thereof will be omitted.

The intra prediction unit 140A includes the adaptive-sub-sampling lumareference pixel acquisition unit 21A, the adaptive-sub-sampling chromareference pixel acquisition unit 22A, the prediction coefficientderivation unit 23, and the chroma linear prediction unit 24 that areshown in FIG. 2, as the intra prediction unit 20A does.

Note that the adaptive-sub-sampling luma reference pixel acquisitionunit 21A provided in the video encoding device AA performs processingappropriate for the encoding unit, whereas the adaptive-sub-samplingluma reference pixel acquisition unit 21A provided in the video decodingdevice BB performs processing appropriate for the decoding unit.

Specifically, in the case where the decoding unit is other than thesmallest CU block, the adaptive-sub-sampling luma reference pixelacquisition unit 21A acquires a pixel value of each reference pixelexisting neighboring the luma block corresponding to the chromaprediction target block to adjust the phase thereof, and outputs thephase-adjusted pixel value as a luma reference pixel value.

On the other hand, in the case where the input image a is an image of anon-YUV420 format and the decoding unit is the smallest CU block, theadaptive-sub-sampling luma reference pixel acquisition unit 21Adetermines the luma intra prediction mode, sub-samples the referencepixels existing neighboring the luma block corresponding to the chromaprediction target block based on the luma intra prediction mode,acquires a pixel value of each of the sub-sampled reference pixels, andoutputs the acquired pixel value as a luma reference pixel value.

Also, the adaptive-sub-sampling chroma reference pixel acquisition unit22A provided in the video encoding device AA performs processingappropriate for the encoding unit, whereas the adaptive-sub-samplingchroma reference pixel acquisition unit 22A provided in the videodecoding device BB performs processing appropriate for the decodingunit.

Specifically, in the case where the decoding unit is other than thesmallest CU block, the adaptive-sub-sampling chroma reference pixelacquisition unit 22A acquires a pixel value of each reference pixelexisting neighboring the chroma prediction target block, and outputs theacquired pixel value as a chroma reference pixel value.

On the other hand, in the case where the input image a is an image of anon-YUV420 format and the decoding unit is the smallest CU block, theadaptive-sub-sampling chroma reference pixel acquisition unit 22Adetermines the luma intra prediction mode, sub-samples the referencepixels existing neighboring the chroma prediction target block based onthe luma intra prediction mode, acquires a pixel value of each of thesub-sampled reference pixels, and outputs the acquired pixel value as achroma reference pixel value.

With the above-described video encoding device AA and video decodingdevice BB, the following effect can be achieved.

In the case where the encoding unit is the smallest CU block, the videoencoding device AA sub-samples, using the adaptive-sub-sampling lumareference pixel acquisition unit 21A, reference pixels existingneighboring the luma block corresponding to the chroma prediction targetblock based on the luma intra prediction mode, thereby sub-samplingthese reference pixels based on the luma component prediction method.Also, in the case where the encoding unit is the smallest CU block, thevideo encoding device AA sub-samples, using the adaptive-sub-samplingchroma reference pixel acquisition unit 22A, reference pixels existingneighboring the chroma prediction target block based on the luma intraprediction mode, thereby sub-sampling these reference pixels based onthe luma component prediction method.

In the case where the decoding unit is the smallest CU block, the videodecoding device BB sub-samples, using the adaptive-sub-sampling lumareference pixel acquisition unit 21A, reference pixels existingneighboring the luma block corresponding to the chroma prediction targetblock based on the luma intra prediction mode, thereby sub-samplingthese reference pixels based on the luma component prediction method.Also, in the case where the decoding unit is the smallest CU block, thevideo decoding device BB sub-samples, using the adaptive-sub-samplingchroma reference pixel acquisition unit 22A, reference pixels existingneighboring the chroma prediction target block based on the luma intraprediction mode, thereby sub-sampling these reference pixels based onthe luma component prediction method.

With the above-described configuration, the video encoding device AA andthe video decoding device BB can halve the number of pixels to bereferenced in order to reduce redundancy among color components, whileconsidering characteristics of an image. Accordingly, the number ofreference pixels to be referenced in order to reduce redundancy amongcolor components can be reduced, while suppressing degradation inencoding performance.

Second Embodiment Configuration and Operations of Video Encoding DeviceCC

A video encoding device CC according to a second embodiment of thepresent invention will be described below. The video encoding device CCis different from the video encoding device AA according to the firstembodiment of the present invention shown in FIG. 1 in that an intraprediction unit 20B is provided in place of the intra prediction unit20A. Note that the same constituent elements of the video encodingdevice CC as those of the video encoding device AA will be assigned thesame signs, and descriptions thereof will be omitted.

The intra prediction unit 20B is different from the intra predictionunit 20A according to the first embodiment of the present inventionshown in FIG. 1 in that an adaptive-sub-sampling luma reference pixelacquisition unit 21B is provided in place of the adaptive-sub-samplingluma reference pixel acquisition unit 21A, and in that anadaptive-sub-sampling chroma reference pixel acquisition unit 22B isprovided in place of the adaptive-sub-sampling chroma reference pixelacquisition unit 22A.

A luma component of a local decoded image f is input to theadaptive-sub-sampling luma reference pixel acquisition unit 21B. Thisadaptive-sub-sampling luma reference pixel acquisition unit 21B alwaysinitially determines a luma intra prediction mode such that the inputimage a is most resembled using the local decoded image f, regardless ofthe encoding unit. Next, the adaptive-sub-sampling luma reference pixelacquisition unit 21B sub-samples reference pixels existing neighboringthe luma block corresponding to the chroma prediction target block basedon the luma intra prediction mode, acquires a pixel value of each of thesub-sampled reference pixels, and outputs the acquired pixel value as aluma reference pixel value h.

A chroma component of the local decoded image f is input to theadaptive-sub-sampling chroma reference pixel acquisition unit 22B. Thisadaptive-sub-sampling chroma reference pixel acquisition unit 22B alwaysinitially determines the luma intra prediction mode such that the inputimage a is most resembled using the local decoded image f, regardless ofthe encoding unit. Next, the adaptive-sub-sampling chroma referencepixel acquisition unit 22B sub-samples reference pixels existingneighboring the chroma prediction target block based on the luma intraprediction mode, acquires a pixel value of each of the sub-sampledreference pixels, and outputs the acquired pixel value as a chromareference pixel value i.

For example, FIG. 10 shows an example in which reference pixels areuniformly sub-sampled in the case where the encoding unit is thesmallest TU block and the input image a is an image of a YUV444 format.

[Configuration and Operations of Video Decoding Device DD]

A video decoding device DD according to a second embodiment of thepresent invention will be described below. The video decoding device DDis different from the video decoding device BB according to the firstembodiment of the present invention shown in FIG. 9 in that an intraprediction unit 140B is provided in place of the intra prediction unit140A. Note that the same constituent elements of the video decodingdevice DD as those of the video decoding device BB are assigned the samesigns, and descriptions thereof will be omitted.

The intra prediction unit 140B includes the adaptive-sub-sampling lumareference pixel acquisition unit 21B, the adaptive-sub-sampling chromareference pixel acquisition unit 22B, the prediction coefficientderivation unit 23, and the chroma linear prediction unit 24, as theintra prediction unit 20B does.

Note that the adaptive-sub-sampling luma reference pixel acquisitionunit 21B provided in the video decoding device DD always determines theluma intra prediction mode, sub-samples reference pixels existingneighboring the luma block corresponding to the chroma prediction targetblock based on the luma intra prediction mode, acquires a pixel value ofeach of the sub-sampled reference pixels, and outputs the acquired pixelvalue as a luma reference pixel value, regardless of the decoding unit.

Also, the adaptive-sub-sampling chroma reference pixel acquisition unit22B provided in the video decoding device DD always determines the lumaintra prediction mode, sub-samples reference pixels existing neighboringthe chroma prediction target block based on the luma intra predictionmode, acquires a pixel value of each of the sub-sampled referencepixels, and outputs the acquired pixel value as a chroma reference pixelvalue, regardless of the decoding unit.

With the above-described video encoding device CC and video decodingdevice DD, the following effect can be achieved in addition to theabove-described effect that can be achieved by the video encoding deviceAA and the video decoding device BB.

The video encoding device CC always sub-samples the reference pixelsregardless of the encoding unit. Also, the video decoding device DDalways sub-samples the reference pixels regardless of the decoding unit.For this reason, the reference pixels can be sub-sampled even in alarger block than the smallest CU block, and accordingly a calculationload of the prediction coefficient derivation unit 23 can be reduced.

Note that the present invention can be achieved by recording, in acomputer-readable non-transitory storage medium, the processing of thevideo encoding device AA/CC and the video decoding device BB/DDaccording to the present invention, and causing the video encodingdevice AA/CC and the video decoding device BB/DD to read and execute aprogram recorded in this storage medium.

Here, for example, a nonvolatile memory such as an EPROM or a flashmemory, a magnetic disk such as a hard disk, a CD-ROM, or the like canbe applied as the aforementioned storage medium. The program recorded inthis storage medium is read and executed by processors provided in thevideo encoding device AA/CC and the video decoding device BB/DD.

The aforementioned program may be transmitted from the video encodingdevice AA/CC and the video decoding device BB/DD in which this programis stored in the storage device to another computer system via atransmission medium or through transmitted waves in the transmissionmedium. Here, the “transmission medium” that transmits the programrefers to a medium having a function of transmitting information, suchas a network (communication network) including the Internet or acommunication line including a telephone line.

The aforementioned program may be for achieving a part of theabove-described functions. Furthermore, the aforementioned program maybe one that can achieve the above-described functions in combinationwith a program that is already recorded in the video encoding deviceAA/CC and the video decoding device BB/DD, i.e., a so-calleddifferential file (differential program).

Although the embodiments of this invention have been described above indetail with reference to the drawings, the detailed configurations arenot limited to these embodiments, and also include designs or the likein the scope that does not depart from the gist of the invention.

For example, in the above-described first embodiment, reference pixelsare sub-sampled based on the luma intra prediction mode in the casewhere the input image a is an image of a non-YUV420 format and theencoding unit or the decoding unit is the smallest CU block. However,the present invention is not limited thereto, and for example, referencepixels may also be sub-sampled based on the luma intra prediction modein the case where the input image a is an image of a YUV420 format andthe encoding unit or the decoding unit is the smallest CU block. Forexample, FIG. 11 shows an example in which reference pixels areuniformly sub-sampled in the case where the input image a is an image ofa YUV420 format.

In the above-described embodiments, reference pixels are sub-sampled tohalve the number thereof, but the invention is not limited thereto andreference pixels may be sub-sampled to reduce the number thereof to 1/nof the number thereof before the sub-sampling (where n is any power oftwo that satisfies n>0). For example, FIGS. 12, 13, and 14 show caseswhere the input image a is an image of a YUV444 format, and referencepixels are sub-sampled to reduce the number thereof to ¼.

In particular, FIG. 12 shows a case where the reference pixels areuniformly sub-sampled. In this example shown in FIG. 12, compared withthe first embodiment of the present invention shown in FIG. 6, the pixelvalue of every other reference pixel is acquired, and both the number ofluma reference pixels and the number of chroma reference pixels are 4pixels. In contrast, in the conventional case of deriving parameters foreach CU, both the number of luma reference pixels and the number ofchroma reference pixels are 16 pixels, as described above using FIGS. 21and 24. Accordingly, the number of reference pixels is ¼ of that in theconventional example.

FIG. 13 shows a case of acquiring pixel values of only reference pixelson the left side of the luma block corresponding to the chromaprediction target block, and reference pixels on the left side of thechroma prediction target block. In this example shown in FIG. 13,compared with the first embodiment of the present invention shown inFIG. 7, the pixel value of every other reference pixel on the left sideof the luma block and the chroma prediction target block is acquired,and both the number of luma reference pixels and the number of chromareference pixels are 4 pixels. Accordingly, the number of referencepixels is ¼ of that in the conventional example.

FIG. 14 shows a case of acquiring pixel values of only reference pixelsabove the luma block corresponding to the chroma prediction targetblock, and reference pixels above the chroma prediction target block. Inthis example shown in FIG. 14, compared with the first embodiment of thepresent invention shown in FIG. 8, the pixel value of every otherreference pixel above the luma block and the chroma prediction targetblock is acquired, and both the number of luma reference pixels and thenumber of chroma reference pixels are 4 pixels. Accordingly, the numberof reference pixels is ¼ of that in the conventional example.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   AA, CC, MM . . . Video encoding device    -   BB, DD, NN . . . Video decoding device    -   20, 20A, 20B, 140, 140A, 140B . . . Intra prediction unit    -   21, 21A, 21B . . . Adaptive-sub-sampling luma reference pixel        acquisition unit    -   22, 22A, 22B . . . Adaptive-sub-sampling chroma reference pixel        acquisition unit    -   23 . . . Prediction coefficient derivation unit    -   24 . . . Chroma linear prediction unit

What is claimed is:
 1. A video encoding device that codes a video imageconfigured to include a plurality of color components, comprising: anintra-frame prediction unit configured to perform intra-frameprediction, the intra-frame prediction unit including: anadaptive-sub-sampling luma reference pixel sub-sampling unit configuredto sub-sample reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; an adaptive-sub-sampling luma reference pixelacquisition unit configured to acquire a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; an adaptive-sub-sampling chromareference pixel sub-sampling unit configured to sub-sample referencepixels existing neighboring the chroma prediction target block based onthe luma intra prediction mode; an adaptive-sub-sampling chromareference pixel acquisition unit configured to acquire a pixel value ofa reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; aprediction coefficient derivation unit configured to derive a predictioncoefficient using the pixel value acquired by the adaptive-sub-samplingluma reference pixel acquisition unit and the pixel value acquired bythe adaptive-sub-sampling chroma reference pixel acquisition unit; and achroma linear prediction unit configured to linearly predict apredictive pixel value of each pixel constituting the chroma predictiontarget block, using a local decoded pixel value of the luma blockcorresponding to the chroma prediction target block and the predictioncoefficient derived by the prediction coefficient derivation unit. 2.The video encoding device according to claim 1, wherein theadaptive-sub-sampling luma reference pixel sub-sampling unit and theadaptive-sub-sampling chroma reference pixel sub-sampling unit furtherconfigured to perform the sub-sampling only in a case where a encodingunit is a predetermined smallest encoding unit.
 3. The video encodingdevice according to claim 1, wherein the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit further configured to always performthe sub-sampling regardless of a encoding unit.
 4. The video encodingdevice according to claim 1, wherein the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit further configured to perform thesub-sampling and reduce the number of reference pixels to 1/n (where nis any power of two that satisfies n>0) of the number of referencepixels before the sub-sampling.
 5. The video encoding device accordingto claim 1, wherein the video image is a video image of a YUV422 format.6. The video encoding device according to claim 1, wherein the size of aprocessing block is 8×8.
 7. A video decoding device that decodes a videoimage configured to include a plurality of color components, comprising:an intra-frame prediction unit further configured to perform intra-frameprediction, the intra-frame prediction unit including: anadaptive-sub-sampling luma reference pixel sub-sampling unit configuredto sub-sample reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; an adaptive-sub-sampling luma reference pixelacquisition unit configured to acquire a pixel value of a referencepixel after the sub-sampling performed by the adaptive-sub-sampling lumareference pixel sub-sampling unit; an adaptive-sub-sampling chromareference pixel sub-sampling unit configured to sub-sample referencepixels existing neighboring the chroma prediction target block based onthe luma intra prediction mode; an adaptive-sub-sampling chromareference pixel acquisition unit configured to acquire a pixel value ofa reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; aprediction coefficient derivation unit configured to derive a predictioncoefficient using the pixel value acquired by the adaptive-sub-samplingluma reference pixel acquisition unit and the pixel value acquired bythe adaptive-sub-sampling chroma reference pixel acquisition unit; and achroma linear prediction unit configured to linearly predict apredictive pixel value of each pixel constituting the chroma predictiontarget block, using a local decoded pixel value of the luma blockcorresponding to the chroma prediction target block and the predictioncoefficient derived by the prediction coefficient derivation unit. 8.The video decoding device according to claim 7, wherein theadaptive-sub-sampling luma reference pixel sub-sampling unit and theadaptive-sub-sampling chroma reference pixel sub-sampling unit furtherconfigured to perform the sub-sampling only in a case where a decodingunit is a predetermined smallest decoding unit.
 9. The video decodingdevice according to claim 7, wherein the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit further configured to always performthe sub-sampling regardless of a decoding unit.
 10. The video decodingdevice according to claim 7, wherein the adaptive-sub-sampling lumareference pixel sub-sampling unit and the adaptive-sub-sampling chromareference pixel sub-sampling unit further configured to perform thesub-sampling and reduce the number of reference pixels to 1/n (where nis any power of two that satisfies n>0) of the number of referencepixels before the sub-sampling.
 11. The video decoding device accordingto claim 7, wherein the video image is a video image of a YUV422 format.12. The video decoding device according to claim 7, wherein the size ofa processing block is 8×8.
 13. A video system including a video encodingdevice that codes a video image configured to include a plurality ofcolor components, and a video decoding device that decodes a video imageconfigured to include a plurality of color components, the videoencoding device including an encoding-side intra-frame prediction unitconfigured to perform intra-frame prediction, the encoding-sideintra-frame prediction unit including: a coding-sideadaptive-sub-sampling luma reference pixel sub-sampling unit configuredto sub-sample reference pixels existing neighboring a luma blockcorresponding to a chroma prediction target block based on a luma intraprediction mode; a coding-side adaptive-sub-sampling luma referencepixel acquisition unit configured to acquire a pixel value of areference pixel after the sub-sampling performed by the encoding-sideadaptive-sub-sampling luma reference pixel sub-sampling unit; acoding-side adaptive-sub-sampling chroma reference pixel sub-samplingunit configured to sub-sample reference pixels existing neighboring thechroma prediction target block based on the luma intra prediction mode;a coding-side adaptive-sub-sampling chroma reference pixel acquisitionunit configured to acquire a pixel value of a reference pixel after thesub-sampling performed by the encoding-side adaptive-sub-sampling chromareference pixel sub-sampling unit; a coding-side prediction coefficientderivation unit configured to derive a prediction coefficient using thepixel value acquired by the encoding-side adaptive-sub-sampling lumareference pixel acquisition unit and the pixel value acquired by theencoding-side adaptive-sub-sampling chroma reference pixel acquisitionunit; and a coding-side chroma linear prediction unit configured tolinearly predict a predictive pixel value of each pixel constituting thechroma prediction target block, using a local decoded pixel value of theluma block corresponding to the chroma prediction target block, and theprediction coefficient derived by the encoding-side predictioncoefficient derivation unit, the video decoding device including adecoding-side intra-frame prediction unit configured to performintra-frame prediction, the decoding-side intra-frame prediction unitincluding: a decoding-side adaptive-sub-sampling luma reference pixelsub-sampling unit configured to sub-sample reference pixels existingneighboring a luma block corresponding to a chroma prediction targetblock based on the luma intra prediction mode; a decoding-sideadaptive-sub-sampling luma reference pixel acquisition unit configuredto acquire a pixel value of a reference pixel after the sub-samplingperformed by the decoding-side adaptive-sub-sampling luma referencepixel sub-sampling unit; a decoding-side adaptive-sub-sampling chromareference pixel sub-sampling unit configured to sub-sample referencepixels existing neighboring the chroma prediction target block based onthe luma intra prediction mode; a decoding-side adaptive-sub-samplingchroma reference pixel acquisition unit configured to acquire a pixelvalue of a reference pixel after the sub-sampling performed by thedecoding-side adaptive-sub-sampling chroma reference pixel sub-samplingunit; a decoding-side prediction coefficient derivation unit configuredto derive a prediction coefficient using the pixel value acquired by thedecoding-side adaptive-sub-sampling luma reference pixel acquisitionunit and the pixel value acquired by the decoding-sideadaptive-sub-sampling chroma reference pixel acquisition unit; and adecoding-side chroma linear prediction unit configured to linearlypredict a predictive pixel value of each pixel constituting the chromaprediction target block, using a local decoded pixel value of the lumablock corresponding to the chroma prediction target block and theprediction coefficient derived by the decoding-side predictioncoefficient derivation unit.
 14. A method for encoding a video image ina video encoding device that codes a video image configured to include aplurality of color components, the video encoding device including anintra-frame prediction unit configured to perform intra-frame predictionand having: an adaptive-sub-sampling luma reference pixel sub-samplingunit; an adaptive-sub-sampling luma reference pixel acquisition unit; anadaptive-sub-sampling chroma reference pixel sub-sampling unit; anadaptive-sub-sampling chroma reference pixel acquisition unit; aprediction coefficient derivation unit; and a chroma linear predictionunit, the method comprising: a first step in which theadaptive-sub-sampling luma reference pixel sub-sampling unit sub-samplesreference pixels existing neighboring a luma block corresponding to achroma prediction target block based on a luma intra prediction mode; asecond step in which the adaptive-sub-sampling luma reference pixelacquisition unit acquires a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; a third step in which the adaptive-sub-samplingchroma reference pixel sub-sampling unit sub-samples reference pixelsexisting neighboring the chroma prediction target block based on theluma intra prediction mode; a fourth step in which theadaptive-sub-sampling chroma reference pixel acquisition unit acquires apixel value of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; a fifthstep in which the prediction coefficient derivation unit derives aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a sixth step in which the chroma linear predictionunit linearly predicts a predictive pixel value of each pixelconstituting the chroma prediction target block, using a local decodedpixel value of the luma block corresponding to the chroma predictiontarget block and the prediction coefficient derived by the predictioncoefficient derivation unit.
 15. A method for decoding a video image ina video decoding device that decodes a video image configured to includea plurality of color components, the video decoding device including anintra-frame prediction unit for performing intra-frame prediction andhaving: an adaptive-sub-sampling luma reference pixel sub-sampling unit;an adaptive-sub-sampling luma reference pixel acquisition unit; anadaptive-sub-sampling chroma reference pixel sub-sampling unit; anadaptive-sub-sampling chroma reference pixel acquisition unit; aprediction coefficient derivation unit; and a chroma linear predictionunit, the method comprising: a first step in which theadaptive-sub-sampling luma reference pixel sub-sampling unit sub-samplesreference pixels existing neighboring a luma block corresponding to achroma prediction target block based on a luma intra prediction mode; asecond step in which the adaptive-sub-sampling luma reference pixelacquisition unit acquires a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; a third step in which the adaptive-sub-samplingchroma reference pixel sub-sampling unit sub-samples reference pixelsexisting neighboring the chroma prediction target block based on theluma intra prediction mode; a fourth step in which theadaptive-sub-sampling chroma reference pixel acquisition unit acquires apixel value of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; a fifthstep in which the prediction coefficient derivation unit derives aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a sixth step in which the chroma linear predictionunit linearly predicts a predictive pixel value of each pixelconstituting the chroma prediction target block, using a local decodedpixel value of the luma block corresponding to the chroma predictiontarget block and the prediction coefficient derived by the predictioncoefficient derivation unit.
 16. A non-transitory computer readablestorage medium storing a program for causing a computer to execute amethod for encoding a video image in a video encoding device that codesa video image configured to include a plurality of color components, thevideo encoding device including an intra-frame prediction unitconfigured to perform intra-frame prediction and having: anadaptive-sub-sampling luma reference pixel sub-sampling unit; anadaptive-sub-sampling luma reference pixel acquisition unit; anadaptive-sub-sampling chroma reference pixel sub-sampling unit; anadaptive-sub-sampling chroma reference pixel acquisition unit; aprediction coefficient derivation unit; and a chroma linear predictionunit, the method comprising: a first step in which theadaptive-sub-sampling luma reference pixel sub-sampling unit sub-samplesreference pixels existing neighboring a luma block corresponding to achroma prediction target block based on a luma intra prediction mode; asecond step in which the adaptive-sub-sampling luma reference pixelacquisition unit acquires a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; a third step in which the adaptive-sub-samplingchroma reference pixel sub-sampling unit sub-samples reference pixelsexisting neighboring the chroma prediction target block based on theluma intra prediction mode; a fourth step in which theadaptive-sub-sampling chroma reference pixel acquisition unit acquires apixel value of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; a fifthstep in which the prediction coefficient derivation unit derives aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a sixth step in which the chroma linear predictionunit linearly predicts a predictive pixel value of each pixelconstituting the chroma prediction target block, using a local decodedpixel value of the luma block corresponding to the chroma predictiontarget block and the prediction coefficient derived by the predictioncoefficient derivation unit.
 17. A non-transitory computer readablestorage medium storing a program for causing a computer to execute amethod for decoding a video image in a video decoding device thatdecodes a video image configured to include a plurality of colorcomponents, the video decoding device including an intra-frameprediction unit configured to perform intra-frame prediction and having:an adaptive-sub-sampling luma reference pixel sub-sampling unit; anadaptive-sub-sampling luma reference pixel acquisition unit; anadaptive-sub-sampling chroma reference pixel sub-sampling unit; anadaptive-sub-sampling chroma reference pixel acquisition unit; aprediction coefficient derivation unit; and a chroma linear predictionunit, the method comprising: a first step in which theadaptive-sub-sampling luma reference pixel sub-sampling unit sub-samplesreference pixels existing neighboring a luma block corresponding to achroma prediction target block based on a luma intra prediction mode; asecond step in which the adaptive-sub-sampling luma reference pixelacquisition unit acquires a pixel value of a reference pixel after thesub-sampling performed by the adaptive-sub-sampling luma reference pixelsub-sampling unit; a third step in which the adaptive-sub-samplingchroma reference pixel sub-sampling unit sub-samples reference pixelsexisting neighboring the chroma prediction target block based on theluma intra prediction mode; a fourth step in which theadaptive-sub-sampling chroma reference pixel acquisition unit acquires apixel value of a reference pixel after the sub-sampling performed by theadaptive-sub-sampling chroma reference pixel sub-sampling unit; a fifthstep in which the prediction coefficient derivation unit derives aprediction coefficient using the pixel value acquired by theadaptive-sub-sampling luma reference pixel acquisition unit and thepixel value acquired by the adaptive-sub-sampling chroma reference pixelacquisition unit; and a sixth step in which the chroma linear predictionunit linearly predicts a predictive pixel value of each pixelconstituting the chroma prediction target block, using a local decodedpixel value of the luma block corresponding to the chroma predictiontarget block and the prediction coefficient derived by the predictioncoefficient derivation unit.